The present invention relates to tank venting control assemblies and particularly to apparatus for controlling the flow of fuel vapor through an aperture in a fuel tank. More particularly, the present invention relates to a tank venting control assembly for selectively discharging fuel vapor pressure in response to the development of high tank pressure conditions and for introducing air into the fuel tank in response to the development of vacuum conditions therein.
Fuel vapor can be created in the fuel tank by temperature differences between the fuel tank and liquid fuel from a fuel pump, as well as by sloshing and agitation of the fuel tank during normal vehicle operation. The pressure buildup resulting from the creation of new fuel vapors must be properly relieved. For this reason, many vehicle fuel systems are equipped with tank venting control assemblies capable of discharging a relatively large amount of fuel vapor in response to the development of high pressure conditions in the fuel tank.
It has long been desirable to maximize the sensitivity that can be achieved with tank venting control assemblies while at the same time minimizing manufacturing costs and assembly difficulties. It would be desirable to provide a tank venting control assembly sensitive enough to begin discharging fuel vapor from the fuel tank in response to pressure differentials as low as about 1-2 inches of water. In fact, a valve design meeting these requirements would closely simulate an open orifice. In any event, meeting the sensitivity requirement calls for a valve which can develop a relatively high actuation force in response to relatively low pressure differentials, long the focus of engineering efforts in this area.
Some tank venting control assemblies have relied upon the use of a small amount of fuel vapor from the fuel tank to provide a pressure signal to actuate the venting assembly, allowing discharge of large volumes of fuel vapor from the fuel tank. Such systems are disclosed, for example, in U.S. Pat. Nos. 4,953,583 and 5,065,782. However, it has proven difficult to design such systems to achieve the desired sensitivity without compromising manufacturability.
In addition to providing for adequate fuel vapor discharge from the fuel tank during high tank pressure conditions, well-designed tank pressure control assemblies must be capable of responding to the reduction of pressure in the fuel tank to below a predetermined level. These tank vacuum conditions are usually relieved by introducing ambient air to the fuel tank to bring the fuel vapor pressure in the fuel tank back to approximately atmospheric pressure. However, it has long been problematic to provide adequate tank vacuum relief functions without complicating the tank venting control assembly unnecessarily.
According to the present invention an apparatus is provided for controlling venting of fuel vapor through an aperture in a fuel tank. The apparatus comprises in part a housing mounted in the aperture and a valve moveable in the housing. The housing is formed to include an outlet and defines a vent path for fuel vapor between the fuel tank and the outlet. The valve is moveable in the housing between the locking position blocking flow of fuel vapor between the fuel tank and the outlet along the vent path in a venting position allowing flow of fuel vapor between the fuel tank and the outlet along the vent path. A spring biases the valve toward its blocking position.
The apparatus also comprises means for using fuel vapor from the fuel tank to move the valve against the spring towards its venting position. The using means includes a venting control chamber receiving fuel vapor from the fuel tank and a conduit communicating fuel vapor from the fuel tank to the venting control chamber. The conduit has a first portion and a second portion moveable relative to the first portion to define an intermediate portion.
The apparatus further comprises a flexible partition extending between the valve in the first portion of the conduit to provide a barrier to prevent fuel vapor venting through the vent path from entering the intermediate portion. The flexible partition is deformable to maintain the barrier when the valve moves away from its blocking position towards its venting position.
Advantageously, according to a preferred aspect of the invention, the conduit extends along a central axis of the housing. The assembly is highly symmetrical about the central axis, simplifying manufacturing and assembly.
Further according to the present invention, an apparatus is provided for controlling venting of fuel vapor through an aperture in a vehicle fuel tank and for introducing air into the fuel tank in response to the development of vacuum conditions therein. The apparatus comprises in part a housing mounted in the aperture and a valve moveable in the housing. The housing is formed to include an outlet, and defines a vent path for fuel vapor between the fuel tank and the outlet. The valve is moveable between the blocking position blocking flow of fuel vapor between the fuel tank and the outlet along the vent path and a venting position allowing flow of fuel vapor between the fuel tank and the outlet along the vent path.
The apparatus further comprises a valve actuator mounted in the housing. The valve actuator is moveable in response to fuel vapor pressure from the fuel tank between a static position allowing the valve to occupy its blocking position and an actuating position urging the valve towards its venting position.
The apparatus further comprises means for slidably coupling the valve actuator to the valve. The slidable coupling means allows the valve to move from its blocking position toward its venting position without moving the valve actuator from its static position to its actuating position in response to the reduction of fuel vapor pressure in the fuel tank below a predetermined level.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.